A technique utilized to reduce the MRI scan time which requires the use of an array coil is:

The correct answer, parallel imaging, is a technique designed to accelerate MRI scans by collecting data from multiple channels simultaneously. This method utilizes an array coil, which consists of multiple receiver coils that can capture signals from different parts of the body at the same time. By leveraging the spatial information obtained from these coils, parallel imaging reduces the amount of time needed for data acquisition without compromising image quality.

Parallel imaging works by undersampling the data and using mathematical algorithms to reconstruct the undersampled images. This allows for shorter scan times, making it advantageous in clinical settings where time efficiency is important.

The other techniques mentioned serve different purposes and do not rely primarily on array coils for acceleration. For example, half Fourier techniques can reduce scan times by only acquiring a portion of the k-space data; however, they do not specifically use array coils to achieve this speed. Similarly, 1/2 NEX (number of excitations) refers to reducing the number of phase-encoding steps to speed up scans but does not utilize multiple coils. Rectangular FOV adjusts the field of view to optimize scanning in certain areas, but again, it does not inherently involve array coils for accelerated imaging.